Biology II - Cell Theory Review

Cell Theory• Term “cell” was coined in 1665 by Robert

Hooke when he looked at a slice of dried cork. He observed that:

1. All living things are made of cells.2. Cells are the smallest “living” unit in

an organism.3. Cells come from previously existing

cells.

Cells - “Fundamental Unit of Life”

Prokaryotes- single celled- no nucleus- no organelles- DNA is a single,

circular molecule- e.g., bacteria

Eukaryotes- single or multicellular- nucleus & nuclear

membrane- organelles present- DNA packaged into

chromosomes- e.g., protozoans,

plants, animals

Cell OrganizationThe cell includes two basic parts:

1. Cell Membrane (outer covering of cell)

2. Cytoplasm (also made of two parts)• Cytosol (fluid portion of the

cytoplasm) • Organelles (organs or functional

parts)

Cell Membrane• Includes:

–Outer boundary–Physical & Chemical Protection–Comprised of two layers of lipid (fat)–Plus Layer of Proteins–Proteins give the cell its unique

function

Cell Membrane

OrganellesEndoplasmic reticulum (ER)• A network of tunnels throughout the cytoplasm

– for cell transport

Golgi Apparatus• Involved in

packaging and secretion of proteins

• Golgi looks like a series of stacked plates.

Mitochondria• Bean shaped, with outer & inner membranes• Cell Powerhouse – produces energy

Cytoskeleton• Skeleton of

the cell• Provides

structure and shape

Plant Cell Organelles• Plants have three special structures not found

in animals: the chloroplast, the cell wall, and the central vacuole.

1. The chloroplast is the site of photosynthesis, the process of converting carbon dioxide into sugar and oxygen using sunlight It uses the green pigment chlorophyll to capture the energy from light.

Plant Cell Organelles2. Each plant cell is surrounded by a rigid cell

wall. The cell wall is outside of the cell membrane. In woody plants, the cell walls can become very thick and rigid.

3. Plant cells also contain a central vacuole, which stores water. It is the storage room of the plant cell.

Nucleus

Nucleus• Control center of cell – “the brain”

• Contains DNA/chromosomes

• Genetic repository for ~ 35,000 genes in humans

• Genes control the synthesis of proteins in each cell, and hence what the cells do.

Human Red Blood Cells

Rat Muscle Cells

Next: Cell Reproduction

Cell Cycle: life and reproduction of a cellPart I - DNA and nuclear division (mitosis) Part II - cytokinesis (cytoplasm duplication)

Cell Cycle: Interphase• Before/Between mitosis• Time of high metabolic activity• “Normal” life of cell

Cell Cycle: Mitosis• Process of cell division (nuclear division) which

produces daughter cells genetically identical to the parent cell

• Four Action Phases (P-M-A-T): prophase, metaphase, anaphase, and telophase, and then the times between mitosis (Interphase).

• Upon completion of the phases of mitosis (nuclear division) the cell “officially” divides into two by a process called cytokinesis - division of cytoplasm and the rest of the cell

InterphaseNot part of mitosisNormal life of the cell

Prophase*Chromosomes coil and condense further.*Nuclear membrane breaks down/ disappears.*Microtubules increase in #, spindle apparatus forms.

Chromosome duplication

Metaphase*Nuclear membrane completely disappeared*Chromosomes move to equator of cell & line up*Chromosomes attach to spindle via kinetochore

Centromeric Region

Anaphase*Movement of chromosomes via microtubulesto opposite sides of the cell. One chromatid to one end the other Chromatid to the opposite end

Telophase*Genetically identical at each pole*Spindle fibers disappear*Chromosomes uncoil*Nuclear envelope reforms

Cytokinesis - is separate from mitosis,= cell/division of cytoplasm.

Mitosis + Cytokinesis result in two identical daughter cells.

Mitosis in a plant cell

Mitosis in an onion root